# I'm beginner and do not how to plot the Basins of attraction by the methods

For a complex polynomial $$P(z)$$, define $$T$$ by $$T(z)=z-\frac{P(z)}{P^{\prime}(z)}$$, where $$P^{\prime}(z)$$ is the first derivative of $$P(z)$$. We consider Newton method for finding the roots of polynomial $$P(z)$$, which is given by the recursive formula

z_{n+1}=T(z_{n}), \ n\in\mathbb{N},\ \ \ \ (16)


where $$T$$ is defined as above. Similarly, we set a new method (and called it S iteration) where $$T$$ is defined as above, by

y_{n}=(1-\beta_{n})z_{n}+\beta_{n}Tz_{n}
z_{n+1}=(1-\alpha_{n})Tz_{n}+\alpha_{n}Ty_{n}, n\in\mathbb{N}, (17)


Now If the sequence $$\{z_n\}_n\in\mathbb{N}$$ (the orbit of the point $$z_1$$) converges to a root $$z^{\ast}$$ of the polynomial $$P$$, then we say that $$z_1$$ is attracted by $$z^{\ast}$$. The attraction basin of the root $$z^{\ast}$$ of the polynomial $$P$$ is the set of all starting points $$z_1$$ which are attracted by $$z^{\ast}$$. If the test polynomial is

P(z) = z^5 + z^4 + z^3 + z^2 + z,  (18)


For this test polynomials $$P(z)$$ above, we consider square domain is centered at the origin in the complex plane as follows

D=[-10,10]\times[-10,10].


If $$\alpha_n=\beta_{n}= 0.8$$ for all $$n \in\mathbb{N}$$ in S iteration method (17), To generate the basins of attraction and to study the dynamics of methods (16) and (17), we divide the domains $$D$$ into 250 × 250 grids. If the sequence $$\{z_n\}_n\in\mathbb{N}$$ attempts a root of polynomial $$P$$ with accuracy of $$10^−4$$ in number of iterations $$n \leq 13$$, then the converging point $$z_0$$ is colored in a color assigned to $$n$$; otherwise, the point is colored in white. Figure 1a, b (see the image in attach or in the link for clear picture https://link.springer.com/article/10.1007/s00500-020-05038-9) represents the obtained basins of attraction by Newton method (16) and S-iteration method (17) for the polynomial $$P$$ defined in (18).

Now the attached pictures are generated by matlab and I want to generate the same pictures in mathematica.

• People here generally like users to post code as Mathematica code instead of just images or TeX, so they can copy-paste it. It makes it convenient for them and more likely you will get someone to help you. You may find the meta Q&A, How to copy code from Mathematica so it looks good on this site, helpful Feb 7 at 0:12
• JuliaSetPlot[z - #/D[#, z] &[z^5 + z^4 + z^3 + z^2 + z], z]? Feb 7 at 0:18

For Newton's method, this could look as follows:

p = z^5 + z^4 + z^3 + z^2 + z
znew = Together[z - p/D[p, z]]

cf = With[{
p = p,
num = N@HornerForm[Numerator[znew]],
denom = N@HornerForm[Denominator[znew]]
},
Compile[{{z0, _Complex}, {maxiter, _Integer}, {\[Epsilon], _Real}},
Block[{iter, z},
z = z0;
iter = 0;
While[Abs[z] > \[Epsilon] && iter < maxiter,
iter++;
z = num/denom
];
iter
],
CompilationTarget -> "C",
RuntimeAttributes -> {Listable},
Parallelization -> True
]
];

n = 1000;
gridpts = Tuples[Subdivide[-10., 10., n - 1], 2] . {1., 1. I};
result = cf[gridpts, 13, 1. 10^-4];

ArrayPlot[Partition[N[result], n],
ColorFunction -> "SunsetColors"
]


• How to write the code for S iteration (17)? Feb 7 at 10:23
• Well, I did mean to get you started, not to solve the problem for you... Feb 7 at 10:24